1. Field of the Invention
The present invention relates to a rear wheel suspension for a vehicle and, more particularly, to a rear wheel suspension for a vehicle which ensures a freedom of layout of the suspension system and can enhance riding comfort and handling safety by minimizing the amount of movement in a transverse direction during up-and-down movement of a wheel and reducing the height of a roll center.
2. Description of Conventional Art
A suspension for a vehicle connects an axle and a car body to each other, and controls a position of a tire with respect to the car body for its optimal position during a vehicle's running. Thus, optimal handling safety may be thereby obtained, and it prevents the axle from directly transmitting impact or vibration from a road surface to the car body. It also prevents damage to cargo, thereby improving riding comfort.
Particularly in a front wheel suspension, the suspension should be designed to absorb vibration or impact from the road surface as well as obtain running safety by maintaining an optimal position in a vehicle's straight ahead position and handling safety in a vehicle's turning position.
The suspension system is structurally characterized as an integral shaft suspension and an independent suspension. The suspension of this invention concerns an independent suspension using a lateral rod that provides restraint against lateral movement.
That is, in the above suspension, rotating power that is applied to the shaft and forces that act in forward and rearward directions are transmitted to a car body through a control rod or a trailing arm. The lateral movement is transmitted to the car body through a lateral rod disposed horizontally with respect to the car body.
Further, steering stability of the vehicle is closely related to the movement of the car body. During the vehicle's running, rolling, pitching, and yawing occur in addition to bounce. These movements should be absorbed to increase the stability and the ride comfort.
In such vibrations, the rolling occurs at a predetermined point when a vehicle is turning, and this point is called a roll center. The variation rate of the roll center's height has an effect on the running safety and steering stability of the vehicle. Accordingly, to achieve running safety, it is more desirable to decrease the variation rate of the roll center's height.
Referring now to FIG. 3 depicting the suspension system using a conventional lateral rod, a buffer 52 that can absorb impact and vibration of each wheel 50 is mounted on an axle beam 51 rotatably supporting wheels 50 in both sides (a suspension system has a different structure in accordance with a suspension mode, and a shock absorber is shown in FIG. 3). A lateral rod 53 disposed laterally with respect to a car body has one end fixed to one side of the axle beam 51 by means of a first elastic bush 54 and the other end fixed to a mounting bracket 55 formed on a lower part of the car body on the opposite side by means of a second elastic bush 56. The lateral rod is thereby disposed at a slant.
The rotating power or forward and rearward forces applied to the axle beam 51 are transmitted to the car body through a control rod or a trailing arm (not illustrated). The up-and-down vibration is absorbed by the buffer 52, and lateral movement is restrained by the lateral rod 53 so that the car body does not vibrate.
In the above suspension system, however, only one lateral rod 53 is provided, and during the up-and-down vibration of the wheels 50 or rolling of the car body, the wheels 50 move upwardly and downwardly moving along a trace of the lateral rod 53 using as a hinge the second elastic bush 56 having a predetermined length, and an amount of movement .alpha. with respect to the lateral direction of the wheels 50 becomes large. The car's straight ahead stability is therefore not very good.
The roll center RC disposed near an intersecting point of the slanting line of the lateral rod 53 and a center line CL of the car body is positioned limitedly on a place (the roll center RC is shown as being positioned on the lateral rod 53 in the drawing, and is actually disposed on the upper portion of the axle beam 51 on a straight line having a slant of the trailing arm that starts from this point. There are restrictions in the freedom of layout of the suspension, and the height of the roll center RC is largely changed by the operation of the lateral rod 53 of a short length during the up-and-down vibration of the wheels 50 to adversely affect the handling safety of the vehicle.
Therefore, in order to solve these problems as mentioned above, it is an object of the present invention to provide a steerable rear wheel suspension which can minimize an amount of movement with respect to the horizontal direction of the wheels during the up-and-down movement of the wheels and reduce the height of the roll center and its variation rate to enhance the freedom of layout and handling safety.